The invention relates generally to a rod wiper or dirt excluder of a linear actuator and, more specifically, to an improved elastomeric annular element surrounding the rod of a hydraulic or pneumatic actuator for excluding dirt from entering the actuator.
Linear actuators are in widespread use in many applications where a linearly directed force is required or useful. Most frequently, the linear actuators are either operated by a pressurized fluid, typically air or hydraulic fluid. Such pneumatic or hydraulic actuators have a rod or ram that is extended and retracted relative to a cylindrical housing. Since the rod extends through an opening in the housing and must move relative to the opening, the possibility exists for environmental materials, such as dirt, to enter the housing through the opening adjacent the rod and interfere with the operation of the actuator. It has become common to use an annular rod wiper element surrounding the rod to assist in excluding dirt and other environmental materials from entering the housing. The wiper element is typically retained in an annular groove in the housing and is biased into close contact with the rod by a variety of means. An example of an annular rod wiper element is described in U.S. Pat. No. 5,257,432. An elastomeric O-ring is used to bias the wiper element into contact with the rod.
While conventional rod wiper elements work effectively under many operating conditions, dirt and other environmental materials can pass the wiper under more severe conditions, for example when there is severe eccentricity of the rod, if the rod flexes under high load or if dirt accumulates on the rod.